Question

f(x)=-1/2x^2+7x-2. x=7. Im trying to find the vertex, one is 7, and the other is 45/2. I keep getting 49/2. what am I missing?

Answer 1

what does "one is 7" mean?

Answer 2

first coordinate of the vertex is always \(-\frac{b}{2a}\)
in your case \(a=-\frac{1}{2},b=7\)

Answer 3

ooh i see "one is 7" means the first coordinate is 7

Answer 4

\[f(7)=-\frac{1}{2}\times 7^2+7\times 7-2\]

Answer 5

that was supposed to be x=7 not one is 7

Answer 6

i see exactly what you are missing
you did not subtract 2 at the end

Answer 7

if I subtract 2 from \[\frac{ 49 }{ 2}\] how does that equal \[\frac{ 45 }{ 2 }\]?

Answer 8

?

Answer 9

the vertex is (7, 45/2). I cant figure out how its not 49/2. the class im in offers no explanation as to how it gets the answers, so im floored on how 7x7 equals 45.

Answer 10

ok lets go slow

Answer 11

did you get that you find the second coordinate of the vertex by finding \[f(7)=-\frac{1}{2}\times 7^2+7\times 7-2\]

Answer 12

yes, I got that far find and this is what I did, in order (7)^2=49. 7x7=49-2=47 so then I have \[-\frac{ 1 }{ 2 }(49)+47\]

Answer 13

you lost me entirely

Answer 14

\[-\frac{1}{2}\times 7^2+7\times 7-2\\
-\frac{1}{2}\times 49+47-2\\
-\frac{49}{2}+\frac{98}{2}-2\\
\frac{49}{2}-2\\
\frac{45}{2}\]

Answer 15

typo there , the second line should have 2 49's in it

Answer 16

just remember

\[-2 =- \frac{4}{2}\]

Answer 17

so you have

\[\frac{49}{2} - \frac{4}{2} = \frac{45}{2}\]

Answer 18

okay thank you I didn't know how to get the second fraction. I see it know. I wish my class program would just explain it seesh. thanks again!